1. Field of the Invention
The present invention relates to a method of manufacturing a chip-type piezoelectric-resonator, in particular, a chip-type piezoelectric resonator which is applied to for example a chip-type filter, oscillator, or discriminator.
2. Description of the Background Art
In general, a piezoelectric-resonator, which is applied to a filter, an oscillator or a discriminator, is provided with lead wires.
In recent years, however, a surface mounting technique has been employed in order to miniaturize an electronic device, leading to a requirement for a chip-type piezoelectric-resonator having no lead wires. A concrete example of such a chip-type piezoelectric-resonator is now described with reference to FIGS. 10 to 12.
As shown in FIGS. 10 to 12, a piezoelectric-resonator 1 comprises a piezoelectric substrate 2. Split vibrating electrodes 3 and 4 are formed on one major surface of the piezoelectric substrate 2, while still another vibrating electrode 5 is formed on another major surface of the substrate 2 so as to be opposite to the vibrating electrodes 3 and 4. These vibrating electrodes 3, 4 and 5 are respectively connected with terminal electrodes 6, 7 and 8, which are located on an edge of the piezoelectric substrate 2.
This piezoelectric-resonator 1 implements an energy trapping type double mode piezoelectric-resonator utilizing a thickness vibration mode having the split vibrating electrodes 3 and 4 and the vibrating electrode 5 which is opposite thereto. Resin plates 11 and 12 of polyphenylene sulfide (PPS), having cavities 9 and 10 in portions corresponding to the vibrating electrodes 3 to 5 respectively, are arranged on both surfaces of the piezoelectric substrate 2, and fixed to the piezoelectric substrate 2 by adhesives 13 and 14 (shown in FIG. 11). As shown in FIG. 12, external electrodes 15, 16 and 17 are formed on an outer surface of the piezoelectric-resonator 1, so as to be electrically connected with the terminal electrodes 6, 7 and 8 respectively.
Such a chip-type piezoelectric-resonator 1 is advantageously miniaturized, so as to enable surface mounting.
However, although the resin plates 11 and 12 are bonded to the piezoelectric substrate 2 by the adhesives 13 and 14, the adhesive strength is relatively weak and hence it is difficult to prevent undesired vibration in a portion other than the vibrating portion of the piezoelectric-resonator 1 for suppressing a spurious response.
Further, employment of the adhesives 13 and 14 may cause permeation of water through interfaces between the piezoelectric substrate 2 and the resin plate 11 and 12, leading to inferiority in moisture resistance.
In addition, the sectional areas of portions of the terminal electrodes 6, 7 and 8, which are exposed on the end surface of the piezoelectric substrate 1, are so small that high reliability cannot be attained in electrical connection between the terminal electrodes 6, 7 and 8 and the external electrodes 15, 16 and 17, respectively.